This invention relates to television cathode ray picture tubes and is particularly directed to means and method for the mounting and implosion-protection of such tubes.
Cathode ray tubes typically have a very high vacuum within the envelope. As a result, several tons of atmospheric pressure are exerted on the envelope, primarily in the areas of face panel and funnel. If there is a weak area in the glass of the envelope such as may result from a scratch or a manufacturing defect, or if the tube receives a blow or a shock, the envelope is susceptible to implosion. (The term "implosion" is defined by Underwriters Laboratories, Incorporated as a "rapid and sudden inward bursting of a high-vacuum glass envelope.")
Several approaches have been evolved to diminish the possibility of implosion, or if an implosion occurs, to reduce its potentially violent effects. An approach presently in common use involves placing a high compressive pre-load on the envelope by means of a tension band, particularly on the skirt area of the face panel. The tension band is under a very high tensive load; for example, 1,500-2,000 pounds. By compressively preloading the face panel, the implosion-induced tensive stresses in the panel must first overcome the compressive pre-stresses in the panel before the panel will fracture. Problems with this method of implosion-protection include the criticality in the placement of the band; for example, a misplacement of the band of one-eighth inch may destroy its implosion protectability. Another problem stems from the fact that the primary pressure is applied at the corners of the face panel, and relatively slight pressure is applied to other parts of the periphery.
Because of their inherent strength and relative stability with respect to the envelope, tension bands have also been used for tube mounting. An L-shaped member is typically installed at each corner, with one leg of the "L" captivated by the tension band, and the other leg extending radially outwardly and having a mounting hole or slot therein for attaching the tube to the television receiver cabinet.
In U.S. Pat. No. 4,210,935, Mitchell et al. discloses an implosion-resistant cathode ray tube. A pair of untensioned half-shell rim bands are affixed on the substantially rectangular shaped face panel flange area. An L-shaped bracket member is disposed intermediate the rim bands and an encircling metal band exerts a compressive force thereon. The base portion of the bracket member is of a size and at a location such that the metal band contacts the rim band on the radius of curvature of the corners and prior to the flattened portion of the flange of the tube envelope.
Krishnamurthy in U.S. Pat. No. 4,121,257 discloses an implosion-protected cathode ray tube which has a first smooth-plastic-coated steel band laid directly on and encircling the glass panel. A second smooth-plastic-coated steel band is laid on the first band. Both bands are tensed to provide hoop compression of the glass panel of the tube. In some embodiments of the Krishnamurthy invention, there may be a lubricating over-coating over the plastic coating and/or a short length of tape under the seal on the first band. Also, the forward edge of the first band may lie over the mold match line or up to 0.300 inch forward of the mold match line of the tube. Krishnamurthy also discloses mounting lugs located at each corner between the bands.
In U.S. Pat. No. 4,135,211, Rogers discloses an implosion-protected, rectangular-type color cathode ray tube comprising a rectangular glass face plate of the type having a viewing window and a flange extending rearwardly therefrom. The bulb has a double tension band system very tightly constricting the flange so as to provide implosion protection for the bulb by compressively pre-loading the corners of the flange. The bulb is characterized by having on the outside of the face plane flange at each corner, and molded integrally with the flange, an incompressible load-concentrating boss for significantly reducing the corner area on which the load is applied by the tension bands. By this expedient, the level of the compressive stresses generated in the flange at the flange corners, and the resultant implosion protection provided by the tension band system, is stated to be greatly enhanced.
Hill et al in U.S. Pat. No. 3,890,464 discloses an impulse-resistant implosion-protection system for large screen cathode ray tubes. The system includes a strip of relatively incompressible tape secured to and encircling the cathode ray tube front panel. A first steel tension band is placed directly over the tape and tensed to provide hoop compression on the front panel. A second steel tension band is placed directly over the first band and also tensed to provide hoop compression on the front panel. The tension bands are tensed so as to provide a relatively high cumulative compression on the front panel.
In U.S. Pat. No. 3,697,686 Hildebrants discloses a glass cathode ray tube envelope provided with implosion-protection means by wrapping the peripheral portion of the envelope adjacent to the faceplate with a piece of fabric impregnated with an uncured thermosetting bonding material. A first steel band is positioned around the tape; two-thirds of the band is heated to bond the tape to the glass envelope and band along two-thirds of the periphery of the envelope. The band is tensioned and permanently mounted on the envelope by welding the ends together under tension while still hot so that, upon cooling, the band tension is increased to about 1,500 pounds. A second steel band is mounted on the first band in the same manner as the first band but with the joint on the opposite side of the envelope to bond the tape to the envelope and the first band along the remaining one-third of the periphery thereof.